(1) Field of the Invention
The present invention relates to a testing device and testing method for a semiconductor integrated circuit (e.g., a LCD driver IC, etc.) that incorporates a multiple number of D/A converters and outputs voltages from the D/A converters via the associated output terminals, and particularly relates to a testing device and testing method which can examine the output voltages from the D/A converters, very quickly with high accuracy.
(2) Description of the Prior Art
With the development of LCD panels into a high precision configuration, LCD driver LSIs incorporated in LCD panels have become developed to deal with a greater number of outputs and a greater number of tones. For such tonal display, each output circuit in the LCD driver LSI incorporates its own D/A converter to output a tonal voltage. For example, a 6 bit D/A converter can display 64 levels of tones while a 8 bit D/A converter can display 256 levels of tones.
Upon the test for such a LCD driver LSI, it is checked if all the tonal voltage levels output from individual D/A converters fall within respective correct ranges and if the values of a tonal voltage level for all D/A converters meet the predetermined uniformity.
FIG. 1 is a conceptual view illustrating a conventional testing method by using a test example of an LCD driver LSI 51 incorporating xe2x80x98mxe2x80x99 output D/A converters 52 each having xe2x80x98nxe2x80x99 tonal levels.
A semiconductor testing device (tester) is used to supply an input signal to an LCD driver LSI 51 so that each D/A converter 52 outputs a voltage level corresponding to the first tonal level. The voltage levels corresponding to the first tonal level are output from associated output terminals (Y1, . . . , Ym) of LCD driver LSI 51 and input to input channels (1ch, . . . , mch) of tester 53. In tester 53, matrix switches 54 are sequentially turned on and off so that the outputs corresponding to the first tonal level are sequentially measured from the first output to the m-th output, one by one, using a high accuracy analog voltage measuring device 55 incorporated in the tester. The measured results are sequentially stored in an incorporated data memory 56. This process is repeated for xe2x80x98nxe2x80x99 tonal levels until all pieces of data relating to all the outputs (m outputs) for all tonal levels (n levels) can be stored into memory 56. As a result, mxc3x97n pieces of data will be stored into memory 56. The data stored in this memory 56 is subjected to a series of logical and arithmetical operations through an unillustrated processing unit incorporated in tester 53 so as to check each tonal voltage value of each output and the uniformity of each tonal voltage level between all the outputs.
In the testing of an LCD driver LSI 51, with the development towards a greater number of outputs and a greater number of tones, the amount of data to be picked up and the time required for data processing increase, so that the testing time increases sharply. Further, increasing the number of tonal levels requires a greater precision for measuring the voltage of each tonal level, needing longer testing time and also an expensive semiconductor testing device incorporating a high precision voltage measuring device.
As stated above, as LCD driver LSIs have become developed to deal with a greater number of outputs and a greater number of tones, the conventional testing method needs a much longer testing time and also needs an expensive semiconductor testing device incorporating a high precision voltage measuring device. Thus, the test cost is increasing more and more.
As a conventional semiconductor testing device to solve the above problems, Japanese Patent Application Laid-Open Hei 9 No.312569 has proposed a semiconductor testing device.
FIG. 2 is a block diagram showing the configuration of the semiconductor testing device disclosed in Japanese Patent Application Laid-Open Hei 9 No.312569.
The D/A converter testing device of this disclosure includes: a digital signal generator 60 for generating n-bit digital data; a clock generator 61; a D/A converter DUT 62 of a device under test which receives the data from digital signal generator 60 and a clock signal from clock generator 61 and outputs an analog signal Vg; a reference (REF) D/A converter 63 which receives the data branched from digital signal generator 60 and the clock signal branched from clock generator 61 and outputs a reference voltage Vref; a differential amplifier 64 receiving the output from D/A converter DUT 62 of the device under test at its one input and the output from reference D/A converter 63 at the other input to effect differential amplification; and a dual comparator 65 which receives the differential amplification output from differential amplifier 64 and checks if the signal in question falls in the allowable range between the upper and lower boundaries. With the above configuration, it is possible to provide a D/A converter testing device that provides a high throughput.
However, the semiconductor testing device (D/A converter testing device) disclosed in Japanese Patent Application Laid-Open Hei 9 No.312569 has suffered from the following difficulties. In the D/A converter testing device shown by Japanese Patent Application Laid-Open Hei 9 No.312569, since the same signals are input to both D/A converter DUT 62 of the device under test and reference D/A converter 63, it is necessary to use a non-defective D/A converter of the device under test for reference D/A converter 63. This is because the number of terminals is different depending upon the number of tones reproduced by the D/A converter of the device under test. Therefore, if a different type of D/A converter is to be tested, there is a need to have an extra non-defective D/A converter of the same type as the D/A converter as a reference D/A converter. The difficulties of the testing device depicted by Japanese Patent Application Laid-Open Hei 9 No.312569 are that there is a need to have a non-defective high-quality reference D/A converter for each type of D/A converter of the device to be tested or for each type of semiconductor integrated circuit incorporating a D/A converter to be tested.
The present invention has been made in view of the above prior art difficulties, and it is therefore an object of the present invention to provide a testing device and testing method for semiconductor integrated circuits which can markedly reduce the test time and enables a conventional inexpensive testing device to perform highly accurate testing without the necessity of providing a separate reference voltage generator for each type of semiconductor integrated circuit to be tested.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a testing device, for a semiconductor integrated circuit which incorporates a multiple number of D/A converters and outputs voltages from the D/A converters via associated output terminals, includes:
a reference voltage generator which generates a multiple number of reference voltages to be compared to each output voltage output from each of the output terminals and can selectively output multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuits;
a multiple number of differential amplifiers, each having two input terminals, one for receiving the output voltage output from the associated output terminal and the other for receiving the reference voltage from the reference voltage generator; and
a comparator that receives the amplified output voltages from the multiple number of differential amplifiers and judges whether the amplified output voltage from each of the differential amplifiers falls within a given voltage range.
In accordance with the second aspect of the present invention, the testing device for semiconductor integrated circuits having the above first feature is characterized in that the reference voltage generator is a D/A converter which receives a digital data signal different from that of the D/A converters incorporated in the semiconductor integrated circuit to generate the multiple number of reference voltages and can selectively output a necessary set of reference voltages from the multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuits, in accordance with the selection of the digital data signal.
The third aspect of the present invention resides in a testing method for a semiconductor integrated circuit which incorporates a multiple number of D/A converters and outputs voltages from the D/A converters via associated output terminals, wherein a testing device for semiconductor integrated circuits is used which comprises:
a reference voltage generator which generates a multiple number of reference voltages to be compared to each output voltage output from each of the output terminals and can selectively output multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuits;
a multiple number of differential amplifiers, each having two input terminals, one for receiving the output voltage output from the associated output terminal and the other for receiving the reference voltage from the reference voltage generator; and
a comparator that receives the amplified output voltages from the multiple number of differential amplifiers and judges whether the amplified output voltage from each of the differential amplifiers falls within a given voltage range, wherein the reference voltage generator includes a D/A converter which receives a digital data signal different from the signals to the D/A converters incorporated in the semiconductor integrated circuit to generate the multiple number of reference voltages and can selectively output a necessary set of reference voltages from the multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuits, in accordance with the selection of the digital data signal,
the method comprising:
the first step for calculating the difference between the reference voltage generated from the reference voltage generator of the testing device and the output voltage output from each output terminal, for all the output terminals;
the second step for amplifying the values obtained from the first step; and
the third step for judging at one time whether all the amplified differential values obtained in the second step in association with respective output terminals fall within the first given voltage range.
In accordance with the fourth aspect of the present invention, the testing method for semiconductor integrated circuits having the above third feature, comprises the above first through third steps and is characterized in that even if the output from the device under test varies, the first given voltage range can be kept at constant by computing the difference between the output from the device under test and the associated reference voltage generated from the above reference voltage.
In accordance with the fifth aspect of the present invention, the testing method for semiconductor integrated circuits having the above third feature, further comprises:
the fourth step for decreasing the width of the first given voltage range by a multiple of the predetermined voltage width to set up a second given voltage range; and
the fifth step for judging at one time whether all the amplified differential values associated to respective output terminals fall within the second given voltage range, and is characterized in that the fourth and fifth steps are repeated until the judgment at the fifth step changes.
In accordance with the sixth aspect of the present invention, the testing method for semiconductor integrated circuits having the above fifth feature is characterized in that, based on the value of the second given voltage range when the judgment at the fifth step changes, the devices under test are classified into a plurality of ranks.
In accordance with the seventh aspect of the present invention, the testing method for semiconductor integrated circuits having the above fifth feature is characterized in that the width of the second given range is made narrower as the above fourth and fifth steps are repeated.
The eighth aspect of the present invention resides in a storage medium for storing the program for a computer to execute a testing method for a semiconductor integrated circuits which incorporates a multiple number of D/A converters and outputs voltages from the D/A converters via associated output terminals, wherein a testing device for semiconductor integrated circuits is used which comprises:
a reference voltage generator which generates a multiple number of reference voltages to be compared to each output voltage output from each of the output terminals and can selectively output multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuits;
a multiple number of differential amplifiers, each having two input terminals, one for receiving the output voltage output from the associated output terminal and the other for receiving the reference voltage from the reference voltage generator; and
a comparator that receives the amplified output voltages from the multiple number of differential amplifiers and judges whether the amplified output voltage from each of the differential amplifiers falls within a given voltage range, wherein the reference voltage generator includes a D/A converter which receives a digital data signal different from the signals to the D/A converters incorporated in the semiconductor integrated circuit to generate the multiple number of reference voltages and can selectively output a necessary set of reference voltages from the multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuit, in accordance with the selection of the digital data signal,
the method comprising:
the first step for calculating the difference between the reference voltage generated from the reference voltage generator of the testing device and the output voltage output from each output terminal, for all the output terminals;
the second step for amplifying the values obtained from the first step; and
the third step for judging at one time whether all the amplified differential values obtained in the second step in association with respective output terminals fall within the first given voltage range, wherein even if the output from the device under test varies, the first given voltage range can be kept at constant by computing the difference between the output from the device under test and the associated reference voltage generated from the above reference voltage.
The ninth aspect of the present invention resides in a storage medium for storing the program for a computer to execute a testing method for a semiconductor integrated circuits which incorporates a multiple number of D/A converters and outputs voltages from the DIA converters via associated output terminals, wherein a testing device for semiconductor integrated circuits is used which comprises:
a reference voltage generator which generates a multiple number of reference voltages to be compared to each output voltage output from each of the output terminals and can selectively output multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuits;
a multiple number of differential amplifiers, each having two input terminals, one for receiving the output voltage output from the associated output terminal and the other for receiving the reference voltage from the reference voltage generator; and
a comparator that receives the amplified output voltages from the multiple number of differential amplifiers and judges whether the amplified output voltage from each of the differential amplifiers falls within a given voltage range, wherein the reference voltage generator includes a D/A converter which receives a digital data signal different from the signals to the D/A converters incorporated in the semiconductor integrated circuit to generate the multiple number of reference voltages and can selectively output a necessary set of reference voltages from the multiple sets of reference voltages required for testing multiple kinds of semiconductor integrated circuit, in accordance with the selection of the digital data signal,
the method comprising:
the first step for calculating the difference between the reference voltage generated from the reference voltage generator of the testing .device and the output voltage output from each output terminal, for all the output terminals;
the second step for amplifying the values obtained from the first step;
the third step for judging at one time whether all the amplified differential values obtained in the second step in association with respective output terminals fall within the first given voltage range, wherein even if the output from the device under test varies, the first given voltage range can be kept at constant by computing the difference between the output from the device under test and the associated reference voltage generated from the above reference voltage;
the fourth step for decreasing the width of the first given voltage range by a multiple of the predetermined voltage width to set up a second given voltage range; and
the fifth step for judging at one time whether all the amplified differential values associated to respective output terminals falls within the second given voltage range,
wherein the fourth and fifth steps are repeated until the judgment at the fifth step changes.
In accordance with the tenth aspect of the present invention, the storage medium for storing the program for a computer to execute the testing method for semiconductor integrated circuits having the above ninth feature is characterized in that, based on the value of the second given voltage range when the judgment at the fifth step changes, the devices under test are classified into a plurality of ranks.
In accordance with the eleventh aspect of the present invention, the storage medium for storing the program for a computer to execute the testing method for semiconductor integrated circuits having the above ninth feature is characterized in that the width of the second given range is made narrower as the above fourth and fifth steps are repeated.
According to the testing device and testing method for semiconductor integrated circuits of the present invention, the output voltage output from the output terminal of each D/A converter in a semiconductor integrated circuit is compared to the reference voltage in each differential amplifier. The results, i.e., the amplified output voltages from the individual differential amplifiers are input in parallel to a comparator. In the comparator, it is judged as to whether the amplified output voltage from each of the differential amplifiers falls within the given voltage range.
According to the testing device and testing method for semiconductor integrated circuits of the present invention, it is possible to markedly reduce the test time by using a comparator which effects simultaneous judgements of all the amplified output voltages, in testing a semiconductor integrated circuit such as a LCD driver LSI which has been developed to deal with a greater number of outputs and a greater number of tones. Further, the testing device of the present invention enables high accuracy testing using a conventional inexpensive tester without the necessity of a high accuracy analog voltage measuring device for voltage measurement as in the conventional configuration, thus making it possible to sharply reduce the testing cost. It is possible to classify the quality of each device based on the variation in voltage output, so that applications of the LCD panel to which the device is applied can be enlarged, thus making it possible to improve the production yield and reducing LCD drivers to fair price. Further, since the reference voltage generator is commonly used for testing multiple kinds of semiconductor integrated circuits, it is no longer necessary to provide a separate reference voltage generator for each type of semiconductor integrated circuit under test. Consequently, the present invention enables only a single testing device to achieve efficient testing of multiple kinds of semiconductor integrated circuits.
The width of the first given voltage range is made narrower by a multiple of the predetermined voltage width to set up a second given voltage range, and it is judged at the same time whether all the differential amplified values from all the associated output terminals fall within the second given voltage range. The devices under test are classified into multiple ranks, based on the second given voltage range which is determined by checking the change in the pass/reject judgement result. Therefore, it is possible to classify the quality of each device based on the variation in voltage output, so that usage of the LCD panel to which the device is applied can be enlarged, thus making it possible to improve the production yield and reducing LCD drivers to fair price.